SA312 EFW Pipe in Lethal Service 1

[ConstantEffort]

I've got a small-diameter lethal service vessel per ASME Section VIII Div 1 with a 316SS metallurgy. I called for ASME SA312-TP316 EFW for the shell and nozzles, with 100% RT.

My code gurus are objecting to the SA312 specification though under two theories:

A) EFW is too similar to ERW. ERW is prohibited in lethal service by UW-2(a).​

-And/Or-​

B) EFW is not a weld since per SA312 it is done without filler metal. Welding, by definition, requires the addition of filler metal.​

I'm past the point of changing anyone's mind except my own... so can you help set me straight?

ERW and EFW differ significantly in process in my view. ERW heats the weld surfaces first, removes the current, and only then presses the molten surfaces together to achieve fusion. No matter how rapid the process, there's an increased potential in ERW for localized lack of fusion since the heat is not applied while the metal is in contact with the mating part. EFW starts with the metal together, applies an arc to create a pool between the two parts, with the pool being established between the two parts before the arc is removed or moves further down the line... EFW is equivalent to GTAW in my mind. No pressure between the parts is needed in EFW.

Autogenous welds are still welds to me. Section IX defines weld as "localized coalescence of metals ... with or without the use of filler metal." It also defines "weld, autogenous" as "a fusion weld made without filler metal."

And bringing it all together, if EFW pipe is infact welded pipe and subject to part UW, and EFW is unique from ERW... why can't I use EFW pipe in a lethal service?

 

[metengr]

SA-312 seam welded pipe can be used for lethal service provided the requirements in UW-2 and Part UW are met.

 

[EdStainless]

The welds in pipe and tube are not fabrication welds per Code, they are part of the material.
Yes there are rules for supplying these for UW service.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

The selection of seam welded pipe has been viewed by the Code committee in the past as being as strong as seamless material if full penetration welded and 100% NDT over the service temperature ranges in Section II, Part D. Over the years, we found that certain seam welded pipe materials failed or developed creep damage or exhibited poor creep rupture ductility because of the long seam weld region.

Because of this, long seam weld strength reduction factors (WSRF) were introduced in various Code book Sections for carbon, low alloy, CSEF, stainless steel and nickel-base alloys. So, these welds are indeed now treated as though they are Code fabricated welds with a separate weld strength reduction factor.

By the way, if you look at autogenously welded stainless steel, the weld strength reduction factor is 1.0 and unchanged over the accepted design temperature range. For welds with filler metal there is a weld strength reduction factor.

 

[EdStainless]

thanks for the addition Metengr, I forgot about that since we do no welding with filler.
In the tubing world all filler added specs are for nuclear applications.

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P.E. Metallurgy, Plymouth Tube

 

[r6155]

I never used welded pipe / tube in nuclear / lethal service.
My good engineering practice is minimum welds as possible.

Regards
r6155

 

[SnTMan]

Yeah, but seamless, stainless pipe is about impossible to get in small quantities. I had not run into this exact situation before, but good to know.

Just so I'm clear, welded pipe is OK for shells & nozzles in lethal service with no additional NDE of the seam on the part of the fabricator?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

@ SnTMan
I prepare specifications thinking about reducing risks, the cost is not the problem in nuclear/lethal service.
I work only with seamless pipe.

Regards
r6155

 

[EdStainless]

We hate making seamless for this service because of all of the ID surface defects. It is very difficult to get to pass a sensitive UT.
Welded and cold drawn tube is the way to go. I wouldn't use tube or pipe that was welded to size, the weld variation will be enough to make NDT difficult also.

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P.E. Metallurgy, Plymouth Tube

 

[SnTMan]

So, from a Code standpoint, welded pipe is OK for shells & nozzles in lethal service with no additional NDE of the seam on the part of the fabricator?

Yes or No?

Regards,

Mike


The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[metengr]

Yes, provide a full RT is performed in accordance with the approved material specification.

 

[moltenmetal]

Seamless can be defective in lots of ways. It can have a horrible bore, and it can be damaged further by improper cleaning and purging prior to the anneal. So buying seamless is no guarantee whatsoever of getting good quality pipe.

Welded seam at least has a clean bore, most of the time...

EdStainless is right- welded and drawn is beautiful stuff.

As to the code NDT requirements, you've been given good advice already.